Telecommunication switching and transmission systems sold today have a fixed-capacity, and, to minimize initial costs, service providers normally purchase systems having a capacity commensurate with, or marginally in excess of, immediate service demands. Typically, service demands grow to exceed the capacity of the purchased system, and telecommunication service providers find it necessary to migrate to larger capacity systems. To minimize additional expense and avoid service disruptions, service providers naturally want to preserve as much of the existing switching and transmission system as possible when expanding to accommodate increased traffic. As a result it is desirable to upgrade current systems, without noticeably impacting existing service. Presently, upgrading a system is a cumbersome, time consuming, labor intensive, and overall expensive undertaking.
A typical upgrade is performed on a telecommunication system by linking an additional telecommunication system to the existing system via a fixed number of hard wired connections called interframe ties. This type of linking does not result in an architecture that guarantees full non-blocking access. That is to say, not all traffic entering one system will be able to gain access to a free output pen on the other system. The degree to which such inter-system access can be obtained is a function of the number of interframe ties between the systems; increasing the ties increases the degree of access. Unfortunately, since each tie monopolizes a port on each system, increasing the number of interframe ties also reduces the overall traffic handling capacity of each system. Therefore, if two systems, each capable of accommodating N lines, are combined using this upgrading technique the resultant system will not support 2N lines. Before performing such an upgrade, the traffic flowing through the system must be carefully analyzed, and the trade-off between non-blocking access and overall traffic handling capacity considered so that the appropriate number of interframe ties may be calculated. As reconfiguring the upgraded system to alter the number of interframe ties is not easily accomplished, the upgraded system cannot be dynamically adapted to respond to subsequent changes in traffic patterns.
Furthermore, prescribed telecommunication standards and/or electrical transmission delay constraints require the additional system introduced in an interframe tie upgrade to be located within a relatively short distance of the existing switching system. As telecommunication equipment requires a substantial amount of floor space, and a fairly large supply of power, such collocation often proves very difficult, if not impossible, at the site of the existing telecommunication system. Another drawback of interframe tie upgrading is the introduction of multiple network operation control points. Both the original and additional systems are basically stand-alone units, each answering to its own controller. In order to harmonize and coordinate the operation of the systems after interframe ties are established, each controller must be linked to an operation support system or supervisory controller (e.g.; a network controller). This multiple controller hierarchy complicates network administration, restoration, provisioning, and monitoring.
As an alternative to upgrading via interframe ties, an existing system may be entirely replaced with a new, larger capacity system. This involves employing additional telecommunication equipment (such as patch panels and/or cross-connects) to temporarily link existing lines to both the new and the old systems, installing a great deal of new cabling to accommodate the new system, and effecting a smooth cut-over of service from the old to the new system (a primarily manual, technically difficult, and error prone process). Naturally, this alternative does not allow for much of the previous telecommunication system be to preserved, since the original switch, the input and output ports, and the cabling leading to and from the switch and ports are rendered useless within the upgraded system.